Wireless communication devices have become smaller and more powerful as well as more capable. Increasingly users rely on wireless communication devices for mobile phone use as well as email and Internet access. At the same time, devices have become smaller in size. In addition, devices may now incorporate multiple transmitters and antennas. These factors may increase a user's exposure to radio frequency (RF) radiation. Devices such as cellular telephones, personal digital assistants (PDAs), laptop computers, and other similar devices provide reliable service with expanded coverage areas. Such devices may be referred to as mobile stations, stations, access terminals, user terminals, subscriber units, user equipments, and similar terms.
A wireless communication system may support communication for multiple wireless communication devices at the same time. In use, a wireless communication device may communicate with one or more base stations by transmissions on the uplink and downlink. Base stations may be referred to as access points, Node Bs, or other similar terms. The uplink or reverse link refers to the communication link from the wireless communication device to the base station, while the downlink or forward link refers to the communication from the base station to the wireless communication devices.
Wireless communication systems may be multiple access systems capable of supporting communication with multiple users by sharing the available system resources, such as bandwidth and transmit power. Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, wideband code division multiple access (WCDMA) systems, global system for mobile (GSM) communication systems, enhanced data rates for GSM evolution (EDGE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Wireless devices may incorporate a system-on-chip (SoC) to perform many of the functions described above. Modern SoCs integrate sensitive analog/radio frequency (RF) blocks on the same die to save space. These sensitive blocks may be located on the same die as noisy digital processing circuits. The switching noise generated by the digital core may propagate through the power and ground distribution network to the analog/RF blocks, causing degraded performance. The problem may be aggravated by technology scaling and package pin count limits because, as more and more transistors and functions are implemented in the same die, there is more switching noise. The problem is compounded by the limited number of power and ground pins, which facilitates noise coupling.
DAC signals are sensitive mixed signals that are susceptible to code dependent noise that appears as a spur in the output spectrum. In some applications the spur desensitizes the receive path in a corresponding band. There is a need in the art for a method and apparatus for attenuating DAC spurs in receive bands.